HYDROLOGICAL LANDSLIDE TRIGGERING IN ASH-COVERED SLOPES OF MANIZALES (COLOMBIA)

A study on hydrological landslide triggering was carried out on ash-co vered slopes near the city of Manizales (Colombia). The saturated hydr aulic conductivity of the different soil types and the pressure head f luctuations in relation to rainfall were determined in order to detect saturated zones in the soil profile which form preferential zones for the development of slip surfaces of landslides. Tensiometer measureme nts revealed saturation in the topsoil as a result of infiltration of rainfall, in the ashes as a result of a perched water table and at the soil-bedrock contact as a result of a goundwater table. The location of the saturated zones in the soil profile proved to be in accordance with the location of slip surfaces observed in the field. Three landsl ides were selected for back analysis to establish the pressure heads t hat could have triggered these landslides. The pressure heads obtained by back analysis were compared with the measured pressure head ranges . The back-calculated pressure heads proved to support the conclusions of the hydrological study.